Study the recursive instance method length()of MyLinkedList2 class and its associated auxiliary method. Then solve (a),...
Study the recursive instance method length()of MyLinkedList2 class and its associated auxiliary method. Then solve (a), (b), and (c) below in a similar way:
(a) Convert the method public Element find(Object obj)of MyLinkedList2 class to a recursive one. Use an auxiliary private method.
(b) Convert the method public String toString( )of MyLinkedList2 class to a recursive one such that it returns the string representation of a linked list in the form:
{ValueDatum1 valueDatum2 valueDatum3 . . . valueDatumN-1 valueDatumN}
Use an auxiliary private method.
(c) Convert the method public insertBefore(Object obj)of MyLinkedList2.Element class to a recursive one. Use an auxiliary private method.
(d) Use the given test program TestMyLinkedList2.java to test your recursive methods.
public class MyLinkedList2 {
protected Element head;
protected Element tail;
public int length(){
return auxLength(head);
}
private int auxLength(Element element){
if(element == null)
return 0;
else
return 1 + auxLength(element.next);
}
public void purge(){
head = null;
tail = null;
}
public Element getHead(){
return head;
}
public Element getTail(){
return tail;
}
public boolean isEmpty(){
return head == null;
}
public Object getFirst(){
if(head == null)
throw new ListEmptyException();
else
return head.datum;
}
public Object getLast(){
if(tail == null)
throw new ListEmptyException();
else
return tail.datum;
}
public void prepend(Object obj){
Element element = new Element(obj, head);
if(head == null)
tail = element;
head = element;
}
public void append(Object obj){
Element element = new Element(obj, null);
if(head == null)
head = element;
else
tail.next = element;
tail = element;
}
public void assign(MyLinkedList2 linkedlist){
if(linkedlist != this) {
purge();
Element element = linkedlist.head;
while (element != null) {
append(element.datum);
element = element.next;
}
}
}
public void extract(Object obj){
Element element = head;
Element lastElement = null;
while(element != null && !
element.datum.equals(obj)){
lastElement = element;
element = element.next;
}
if(element == null)
throw new IllegalArgumentException("item not found");
if(element == head)
head = element.next;
else
lastElement.next = element.next;
if(element == tail)
tail = lastElement;
}
public void extractFirst(){
if(head == null)
throw new IllegalArgumentException("item not found");
head = head.next;
if(head == null)
tail = null;
}
public void extractLast() {
if(tail == null)
throw new IllegalArgumentException("item not found");
if(head == tail)
head = tail = null;
else {
Element previous = head;
while (previous.next != tail)
previous = previous.next;
previous.next = null;
tail = previous;
}
}
public String toString(){
String s = "{";
boolean first = true;
Element element = head;
while (element != null){
if(first){
first = false;
s += element.datum;
}
else
s += ", "+element.datum;
element = element.next;
}
s += "}";
return s;
}
public Element find(Object obj){
Element element = head;
while(element != null){
if(element.datum.equals(obj))
return element;
element = element.next;
}
return null;
}
void append(Integer integer) {
throw new UnsupportedOperationException("Not supported yet."); //To
change body of generated methods, choose Tools | Templates.
}
public final class Element{
Object datum;
Element next;
Element(Object obj, Element element){
datum = obj;
next = element;
}
public Object getDatum(){
return datum;
}
public Element getNext(){
return next;
}
public void insertAfter(Object obj){
next = new Element(obj, next);
if(this == tail)
tail = next;
}
public void insertBefore(Object obj){
Element element = new Element(obj, this);
if(this == head){
head = element;
return;
}
Element previousElement = head;
while(previousElement != null && previousElement.next !=
this){
previousElement =
previousElement.next;
}
previousElement.next = element;
}
public void extract(){
Element element = null;
if(this == head)
head = next;
else{
element = head;
while(element != null && element.next != this){
element =
element.next;
}
if(element == null)
throw new InvalidOperationException();
element.next = next;
}
if(this == tail)
tail = element;
}
}
}
--------------------
import java.util.Scanner;
import lab5.*;
public class TestMyLinkedList2
{
public static void main(String[] args){
Scanner stdin = new
Scanner(System.in);
MyLinkedList2 list = new
MyLinkedList2();
int i = 1;
String inputLine;
System.out.print("Enter integer
value#"+ i+ " (or press q to quit): ");
while(stdin.hasNextInt()){
list.append(new
Integer(stdin.nextInt()));
System.out.print("Enter integer
value#"+ ++i + " (or press q to quit): ");
}
stdin.next(); // discard the
character used to terminate the above loop
System.out.println("The list is: "
+ list);
System.out.println("The list's
length is: " + list.length());
if(! list.isEmpty()){
System.out.print("Enter the integer value to be searched for:
");
MyLinkedList2.Element element =
list.find(new Integer(stdin.nextInt()));
if(element ==
null)
System.out.println("NOT FOUND");
else{
System.out.println("FOUND");
System.out.print("Enter the integer value to be inserted before the
found element: ");
element.insertBefore(new Integer(stdin.nextInt()));
System.out.println("The list is: " + list);
}
}
}
}
Homework Answers
Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks
// MyLinkedList2.java (modified)
public class MyLinkedList2 {
protected Element head;
protected Element tail;
public int length() {
return auxLength(head);
}
private int auxLength(Element element) {
if (element == null)
return 0;
else
return 1 + auxLength(element.next);
}
public void purge() {
head = null;
tail = null;
}
public Element getHead() {
return head;
}
public Element getTail() {
return tail;
}
public boolean isEmpty() {
return head == null;
}
public Object getFirst() {
if (head == null)
throw new ListEmptyException();
else
return head.datum;
}
public Object getLast() {
if (tail == null)
throw new ListEmptyException();
else
return tail.datum;
}
public void prepend(Object obj) {
Element element = new Element(obj, head);
if (head == null)
tail = element;
head = element;
}
public void append(Object obj) {
Element element = new Element(obj, null);
if (head == null)
head = element;
else
tail.next = element;
tail = element;
}
public void assign(MyLinkedList2 linkedlist) {
if (linkedlist != this) {
purge();
Element element = linkedlist.head;
while (element != null) {
append(element.datum);
element = element.next;
}
}
}
public void extract(Object obj) {
Element element = head;
Element lastElement = null;
while (element != null && !element.datum.equals(obj)) {
lastElement = element;
element = element.next;
}
if (element == null)
throw new IllegalArgumentException("item not found");
if (element == head)
head = element.next;
else
lastElement.next = element.next;
if (element == tail)
tail = lastElement;
}
public void extractFirst() {
if (head == null)
throw new IllegalArgumentException("item not found");
head = head.next;
if (head == null)
tail = null;
}
public void extractLast() {
if (tail == null)
throw new IllegalArgumentException("item not found");
if (head == tail)
head = tail = null;
else {
Element previous = head;
while (previous.next != tail)
previous = previous.next;
previous.next = null;
tail = previous;
}
}
public String toString() {
// calling helper method to perform recursion and return the string in
// specified form
String s = "{" + auxToString(head) + "}";
return s;
}
// method to find and return the string representation of the list using
// recursion
private String auxToString(Element element) {
if (element == null) {// empty element, base condition
return "";// returning empty string
} else {
// storing datum's string value in a String variable
String str = element.datum.toString();
// appending a white space if there is a next element
if (element.next != null) {
str += " ";
}
// appending str with auxToString() value of next element and
// returns it
return str + auxToString(element.next);
}
}
public Element find(Object obj) {
// calling auxiliary method to perform recursion and find the element
return auxFind(obj, head);
}
// actual method that does recursion to find an element with given object if
// exists
private Element auxFind(Object obj, Element element) {
if (element == null) {// base case 1
return null;// not found
}
if (element.datum.equals(obj)) {// base case 2
return element;// found
}
// recursing to find obj
return auxFind(obj, element.next);
}
void append(Integer integer) {
append((Object) integer);
}
public final class Element {
Object datum;
Element next;
Element(Object obj, Element element) {
datum = obj;
next = element;
}
public Object getDatum() {
return datum;
}
public Element getNext() {
return next;
}
public void insertAfter(Object obj) {
next = new Element(obj, next);
if (this == tail)
tail = next;
}
public void insertBefore(Object obj) {
Element element = new Element(obj, this);
if (this == head) {
head = element;
return;
}
// taking a reference to head node
Element previousElement = head;
// calling recursive function to add element before this
auxInsertBefore(previousElement, element);
}
// helper method which actually does the recursion. This will find the
// previous node of this node and adds Element toAdd as the next of that
// node
private void auxInsertBefore(Element prev, Element toAdd) {
// checking if the next node of prev is this node (base case)
if (prev.next == this) {
// found, adding toAdd element as the next of prev
prev.next = toAdd;
} else {
// recursing with next value of prev
auxInsertBefore(prev.next, toAdd);
}
}
public void extract() {
Element element = null;
if (this == head)
head = next;
else {
element = head;
while (element != null && element.next != this) {
element = element.next;
}
if (element == null)
throw new InvalidOperationException();
element.next = next;
}
if (this == tail)
tail = element;
}
}
}
/*OUTPUT of given test program*/
Enter integer value#1 (or press q to quit): 3
Enter integer value#2 (or press q to quit): 2
Enter integer value#3 (or press q to quit): 5
Enter integer value#4 (or press q to quit): 7
Enter integer value#5 (or press q to quit): 8
Enter integer value#6 (or press q to quit): q
The list is: {3 2 5 7 8}
The list's length is: 5
Enter the integer value to be searched for: 7
FOUND
Enter the integer value to be inserted before the found element: 33
The list is: {3 2 5 33 7 8}
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